Photographic material containing yellow fog-preventing agents



Claims. (u. es-s4 ABTRA CT BF THE DESCLQSURE Yellow fog formation in silver halide emulsion supports, particularly where the support surface is a baryta layer, can be avoided by adding to the emulsion or baryta layer or both a compound having the formula R-(s-C-RQ,

wherein R is a pyrimidine or a thiodiazole ring; R an alkyl group having 1 to 18, preferably 6 to 18 carbon atoms, a CYClOfillQ/l group, preferably a six rnembered cycloalkyl group such as cyclohexyl, an aralkyl group, such as benzyl, and an aryl group, such as phenyl, naphthyl; n an integer from 1 to 2, said radical -S-fil-R being bonded to a carbon atom of the heterocyclic ring, which carbon atom is in alpha position to a heterocyclic nitrogen atom.

This invention relates to an improved photographic material comprising a silver halide emulsion layer and containing an organic compound which is capable of preventing the formation of yellow fog.

In the processing of photographic materials, thiosulfate is frequently transferred from the fixing bath into the developer. On other occasions, such as when using highspeed, stabilizing or fixing developers, a silver halide solvent, generally thiosulfate, is added to the developer. When such developers containing silver halide solvents are used in the development of photographic materials, a yellow to brown fogging is produced, of varying intensity depending on the type and the age of the photographic paper. In the presence of many stabilizers, e.g., l- -henyl- S-mcrcapto-tetrazole, this fogging may also be blue to bluish violet in color. With photographic papers, this fogging is due to finely divided silver deposited in the barytacoating.

This yellow fogging produced with baryta-coated photographic papers results from the passing, during the casting process, of silver salts from the silver halide emulsion into the baryta coating where they are adsorbed by the baryta. During the storage of the papers, these silver salts are reduced to silver, particularly in the first months of storage. It the developer used in the processing of such papers contains silver halide solvents. such as thiosulfates, the dissolved silver salts are reduced on the silver nuclei of the baryta and a ye low fogging and spot formation is produced. Furthermore, the properties of the starting materials play a large part in the formation of spots or stains.

After storage, the yellow fogging appears particularly strongly at those areas of the papers which were exposed to the humidity of the air, i.e., at the edges of the papers and on the uppermost sheet of a pack.

This yellow fogging occurs particularly when using unwashed silver chloride or chlorobromide emulsions because the chlorides present in excess are able to form soluble silver complex salts.

aired States Patent 0 The yellow fogging also occurs, if, in the production of the emulsion or the balyta, types of gelatin are used which contain compounds capable of dissolving silver halide and if in addition nucleus-forming degradation products of the gelatin are present. Such types of gelatin also cause a yellow fogging with photographic films. In addition, emulsions which have only just ripened and have a steep gradation are particularly liable to produce yellow fogging when steeply operating developers with a relatively high content of potassium bromide are used for developing the silver image.

It has now been found that the formation of yellow fog in photographic materials comprising water permeable colloid layers including a silver halide emulsion layer and preferably also a baryta layer can be avoided by using photographic materials which contain in at least one of said colloid layers a heterocyclic compound selected from the group consisting of rnercapto pyrimidines and mercapto thiodiazoles, in which the hydrogen atom of the mercapto group is replaced by an acyl group derived from an organic carboxylic acid containing 2 to 19, preferably 7 to 19 carbon atoms.

These heterocyclic compounds may be illustrated by the following general formula:

I Rae-$4M wherein:

R is a pyrimidine or a thiodiazole ring,

R an alkyl group having 1 to 18, preferably 6 to 18 carbon atoms, a cycloalkyl group, preferably a six membered cycloalkyl group such as cyclohexyl, an aralkyl group, such as benzyl, and an aryl group, such as phenyl, naphthyl,

n an integer from 1 to 2,

said radical SCR1 being bonded to a carbon atom of the heterocyclic ring, which carbon atom is in a-position to a hetenocyclic nitrogen atom.

More specifically these heterocyclic compounds may be illustrated by the following formulae:

wherein R has the same meaning as in Formula I and R stands for any of the R groups.

Specific examples of suitable compounds are illustrated by the following formulae:

0 M. P. 103 C.

The compounds may be produced by reacting the corresponding mercapto pyrimidines and mercapto thiodiazoles with carboxylic acid chlorides in the presence of sodium hydroxide in acetone at temperatures of to C. If the heterocyclic compounds contain a single mercapto group the heterocyclic compounds and the carboxylic acid chlorides are applied in equimolar amounts. If the heterocyclic compounds contain two mercapto groups two mols of carboxylic acid chloride are used per mol of heterocyclic compound. The raw products obtained are purified by washing them with water and methanol or by recrystallizing them from ethanol and extracting them with ether. The preparation of these compounds is illustrated by the following examples:

Production of Compound 3.--l5.5 g. A mol) of 6-methyl-2,4-mercapto pyrimidine are suspended in a mixture of 200 ml. of acetone and 40 ml. of 5 N NaOH.

28.1 g. A mol) of benzoyl chloride are added to the mixture dropwise while stirring at a temperature of 0 to 5 C. within 15 minutes. The reaction mixture is stirred for 3 hours further at room temperature. The product which has formed is filtered, recrystallized from 440 cc. of ethanol and extracted with ether for further purification. Yield: 12 g.; MP. 105 C.

Production of Compound 7.26.2 g. mol) of 2-octylthio-5-mercapto thiodiazole-1,3,4 are suspended in a mixture of 300 ml. of acetone and 20 ml. of 5 N NaOH. The mixture has added thereto dropwise while stirring at temperatures of 0 to 5 C. a solution of 21.8 g. mol) of lauric acid chloride in 50 ml. of acetone. The precipitate which has formed is sucked off and washed with water and methanol. Yield: 31 g.; M.P. 54 C.

These substances are probably not adsorbed by the silver halide grains of the emulsion, but are disposed in gelatin phase between the silver halide grains. In the alkaline developer, the carboxy group is split off and the compound reacts with the soluble silver salts, thus preventing the formation of yellow fogging.

As silver halide emulsion, it is possible to use emulsions containing silver chloride or silver bromide or mixtures thereof. Furthermore, the emulsion may contain 4 up to about 10% of silver iodide, as calculated on total silver halide.

As binding agents for the baryta layer can be used animal glues preferably gelatin which may be partially replaced by film-forming hydrophilic products such as polyvinyl alcohol, polyvinyl-pyrrolidone, alginic acid or derivatives thereof such as alkali metal salts, esters in particular with lower aliphatic glycols, or amides, turthermore carboxyethylcellulose, starch or the like. As baryta pigment can be used mineral products such as processed heavy spar or artificial products such as permanent white or blanc fixe.

The compounds according to the invention can be added to any desired layer of the photographic material, but advantageously to the baryta and/or light-sensitive silver halide emulsion layer. It will depend on the photographic material and the compound in which layer the optimum eflicacy is achieved. However, this can be established by a few simple experiments Without any difiiculties.

The same applies as regards the concentration to be used. The quantities to be added depend on the layer in which the compounds are incorporated and this can also be established by simple tests. When used in the emulsion layer, the compounds are added in amounts of about 2-300 mg, advantageously 5-60 mg. per mol of silver halide. For the baryta layer, concentrations of 0.0ll.0 g./l. and advantageously 0.05-0.15 g./l. of casting solution are suitable. These amounts correspond to 0.02-2 mg., preferably 0.040.3 mg. per gram of barium sulfate.

The compounds according to the invention can be added at any time, but advantageously to the prepared casting solution.

The photographic emulsions can be either sensitized or non-sensitized optically. In addition, other chemical ripening compounds can also be added to them, for example sulfur compounds or noble metal salts. The emulsions can further contain alkylene oxide polymerization products as chemical sensitizers. Moreover, the new stabilizers can be used together with other stabilizers which are already known. They can furthermore be used in emulsions which contain color couplers or silver halide developer substances.

In the processing of the photographic materials according to the invention, it is possible to employ the conventional developer combinations. The process does not depend on any particular developer substances. It is for example possible to use as developer substances hydroquinone, pyrocatechol, p-methylaminophenyl, l-phenyl- 3-pyrazolidones or phenylene diamines.

EXAMPLE 1 An unrinsed silver chlorobromide emulsion containing 0.12 mol of silver halide per liter, has added thereto prior to casting 50 mg. of Compound 7 dissolved in alcohol. After adding the conventional hardening and wetting agents, the emulsion is then applied in known manner to a baryta-coated paper and dried. The paper, both when fresh and after being kept for 2 days in a hot cupboard at 60 C., was developed for l, 2, 3, 5 and 7 minutes at 30 C. in a pnethylaminophenol-hydroquinone developer, to which 10 g./l. of crystallized sodium thiosulfate had been added in order to test for yellow fogging. Whereas the specimen showed no yellow fogging, even after storage in the heated cupboard, a control specimen when fresh showed a slight yellow fogging, and after being kept in the cupboard a strong brownish-yellow fogging was visible, even after a development time of 1 minute. If the emulsion layer is removed from the baryta coating, it is seen that the baryta coating of the control specimen is brown in color and that of the test specimen is colorless.

Instead of Compound 7 referred to above, 30 mg./l. of 2-octylthio S-benzoylthio-1,3, 4-thiodiazole can also be added to the emulsion with the same result.

EXAMPLE 2 One liter of silver chloride emulsion containing 0.08 mol of silver halide, has 50 mg. of Compound 2, dissolved in alcohol, added thereto prior to casting. After adding the usual hardening and wetting agents, the emulsion is then applied in known manner to a baryta-coated paper and dried. The test for yellow fogging is carried out as described in Example 1. Whereas the control specimen shows a bluish-yellow fogging after beirz kept in the heated cupboard, no fogging is visible with the specimen according to the invention.

EXAMPLE 3 A phototechnical emulsion, which contains about 0.4 mol./l. of silver halide (silver iodobromide emulsion), has 5 of Compound 6, dissolved in alcohol, added thereto prior to casting. After adding the usual hardening and wetting agents, the emulsion is applied in known manner to a film or paper support and dried.

The test for yellow fogging is carried out as described in Example 1. The specimen does not show any yellow fogging, whereas a yellow fogging is visible on the control specimen after being stored in the heated cupboard.

EXAMPLE 4 A baryta-coating solution has added thereto 0.1 g./l. of Compound 7 or 0.05 g./1. of Compound 2, dissolved in alcohol, and a paper is baryta-coated therewith three times in known manner. An unrinsed silver chlorobromide emulsion is thereafter applied to this paper in known manner.

The baryta-coating solution may be obtained in known manner from kg. of barium sulfate (containing of water), 1.5 kg. of gelatine in the form of a 5% aqueous solution, 100 cm. or" a 20% aqueous sodium hexametaphosphate solution, 300 cm. of a 10% aqueous chrome alum solution and 200 cm. of milk.

The test for yellow fogging is carried out as described in Example 1. Whereas the experimental samples shows no yellow fogging after r e heated chamber storage, a dark brown patchy yellow fogging is visible with the control specimen.

What I claim is:

1. A photographic material comprising a support, having coated thereon hydrophilic water permeable colloid layers including a light-sensitive silver halide emulsion layer, at least one of said colloid layers containing a heterocyclic compound selected from the group consisting of mercapto pyrimidines and mercapto thiodiazoles in which the hydrogen atom of the mercapto group is replaced by an acyl group of an organic carboxylic acid containing 2 to 19 carbon atoms, said compound being present in amount suflicient to inhibit the formation of yellow fog.

2. A photographic material according to claim 1, wherein one of said colloid layer is a baryta layer which is arranged between the support and the silver halide emulsion layer.

3. A photographic material according to claim 1, wherein said heterocyclic compound is a compound of the general formula wherein R and R stand for an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an aralkyl group or an aryl group.

References Cited UNITED STATES PATENTS 2,285,410 6/1942 Bousquet et al. 260302 2,760,933 8/1956 Fields et al 2 302 2,319,965 1/1958 Murray et al. 96l09 2,939,789 6/1960 Dersch et a1. 96109 3,051,570 8/1962 Dersch et al. 96109 NORMAN G. TORCHIN, Primary Examiner.

E. H. RA-UBITSCHEK, Assistant Examiner. 

